1 /* $OpenBSD: getentropy_linux.c,v 1.28 2014/07/20 03:24:10 deraadt Exp $ */
2
3 /*
4 * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org>
5 * Copyright (c) 2014 Bob Beck <beck@obtuse.com>
6 *
7 * Permission to use, copy, modify, and distribute this software for any
8 * purpose with or without fee is hereby granted, provided that the above
9 * copyright notice and this permission notice appear in all copies.
10 *
11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18 *
19 * Emulation of getentropy(2) as documented at:
20 * http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2
21 */
22
23 #define _POSIX_C_SOURCE 199309L
24 #define _GNU_SOURCE 1
25 #include <sys/types.h>
26 #include <sys/param.h>
27 #include <sys/ioctl.h>
28 #include <sys/resource.h>
29 #include <sys/syscall.h>
30 #ifdef HAVE_SYS_SYSCTL_H
31 #include <sys/sysctl.h>
32 #endif
33 #include <sys/statvfs.h>
34 #include <sys/socket.h>
35 #include <sys/mount.h>
36 #include <sys/mman.h>
37 #include <sys/stat.h>
38 #include <sys/time.h>
39 #include <stdlib.h>
40 #include <stdint.h>
41 #include <stdio.h>
42 #include <link.h>
43 #include <termios.h>
44 #include <fcntl.h>
45 #include <signal.h>
46 #include <string.h>
47 #include <errno.h>
48 #include <unistd.h>
49 #include <time.h>
50 #ifdef HAVE_OPENSSL
51 #include <openssl/sha.h>
52 #endif
53
54 #include <linux/random.h>
55 #include <linux/sysctl.h>
56 #ifdef HAVE_GETAUXVAL
57 #include <sys/auxv.h>
58 #endif
59 #include <sys/vfs.h>
60
61 #define REPEAT 5
62 #define min(a, b) (((a) < (b)) ? (a) : (b))
63
64 #define HX(a, b) \
65 do { \
66 if ((a)) \
67 HD(errno); \
68 else \
69 HD(b); \
70 } while (0)
71
72 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
73 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
74 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
75
76 int getentropy(void *buf, size_t len);
77
78 static int gotdata(char *buf, size_t len);
79 #ifdef SYS__getrandom
80 static int getentropy_getrandom(void *buf, size_t len);
81 #endif
82 static int getentropy_urandom(void *buf, size_t len);
83 #ifdef SYS__sysctl
84 static int getentropy_sysctl(void *buf, size_t len);
85 #endif
86 #ifdef HAVE_OPENSSL
87 static int getentropy_fallback(void *buf, size_t len);
88 static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data);
89 #endif
90
91 int
getentropy(void * buf,size_t len)92 getentropy(void *buf, size_t len)
93 {
94 int ret = -1;
95
96 if (len > 256) {
97 errno = EIO;
98 return -1;
99 }
100
101 #ifdef SYS__getrandom
102 /*
103 * Try descriptor-less getrandom()
104 */
105 ret = getentropy_getrandom(buf, len);
106 if (ret != -1)
107 return (ret);
108 #endif
109
110 /*
111 * Try to get entropy with /dev/urandom
112 *
113 * This can fail if the process is inside a chroot or if file
114 * descriptors are exhausted.
115 */
116 ret = getentropy_urandom(buf, len);
117 if (ret != -1)
118 return (ret);
119
120 #ifdef SYS__sysctl
121 /*
122 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
123 * sysctl is a failsafe API, so it guarantees a result. This
124 * should work inside a chroot, or when file descriptors are
125 * exhuasted.
126 *
127 * However this can fail if the Linux kernel removes support
128 * for sysctl. Starting in 2007, there have been efforts to
129 * deprecate the sysctl API/ABI, and push callers towards use
130 * of the chroot-unavailable fd-using /proc mechanism --
131 * essentially the same problems as /dev/urandom.
132 *
133 * Numerous setbacks have been encountered in their deprecation
134 * schedule, so as of June 2014 the kernel ABI still exists on
135 * most Linux architectures. The sysctl() stub in libc is missing
136 * on some systems. There are also reports that some kernels
137 * spew messages to the console.
138 */
139 ret = getentropy_sysctl(buf, len);
140 if (ret != -1)
141 return (ret);
142 #endif /* SYS__sysctl */
143
144 /*
145 * Entropy collection via /dev/urandom and sysctl have failed.
146 *
147 * No other API exists for collecting entropy. See the large
148 * comment block above.
149 *
150 * We have very few options:
151 * - Even syslog_r is unsafe to call at this low level, so
152 * there is no way to alert the user or program.
153 * - Cannot call abort() because some systems have unsafe
154 * corefiles.
155 * - Could raise(SIGKILL) resulting in silent program termination.
156 * - Return EIO, to hint that arc4random's stir function
157 * should raise(SIGKILL)
158 * - Do the best under the circumstances....
159 *
160 * This code path exists to bring light to the issue that Linux
161 * does not provide a failsafe API for entropy collection.
162 *
163 * We hope this demonstrates that Linux should either retain their
164 * sysctl ABI, or consider providing a new failsafe API which
165 * works in a chroot or when file descriptors are exhausted.
166 */
167 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
168 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
169 raise(SIGKILL);
170 #endif
171 #ifdef HAVE_OPENSSL
172 ret = getentropy_fallback(buf, len);
173 if (ret != -1)
174 return (ret);
175 #endif
176
177 errno = EIO;
178 return (ret);
179 }
180
181 /*
182 * Basic sanity checking; wish we could do better.
183 */
184 static int
gotdata(char * buf,size_t len)185 gotdata(char *buf, size_t len)
186 {
187 char any_set = 0;
188 size_t i;
189
190 for (i = 0; i < len; ++i)
191 any_set |= buf[i];
192 if (any_set == 0)
193 return -1;
194 return 0;
195 }
196
197 #ifdef SYS__getrandom
198 static int
getentropy_getrandom(void * buf,size_t len)199 getentropy_getrandom(void *buf, size_t len)
200 {
201 #if 0
202
203 /* Hand-definitions until the API becomes commonplace */
204 #ifndef SYS__getrandom
205 #ifdef __LP64__
206 #define SYS__getrandom 317
207 #else
208 #define SYS__getrandom 354
209 #endif
210 #endif
211 struct __getrandom_args args = {
212 .buf = buf;
213 .len = len;
214 .flags = 0;
215 };
216
217 if (len > 256)
218 return (-1);
219 ret = syscall(SYS__getrandom, &args);
220 if (ret == len)
221 return (0);
222 #endif
223 return -1;
224 }
225 #endif
226
227 static int
getentropy_urandom(void * buf,size_t len)228 getentropy_urandom(void *buf, size_t len)
229 {
230 struct stat st;
231 size_t i;
232 int fd, cnt, flags;
233 int save_errno = errno;
234
235 start:
236
237 flags = O_RDONLY;
238 #ifdef O_NOFOLLOW
239 flags |= O_NOFOLLOW;
240 #endif
241 #ifdef O_CLOEXEC
242 flags |= O_CLOEXEC;
243 #endif
244 fd = open("/dev/urandom", flags, 0);
245 if (fd == -1) {
246 if (errno == EINTR)
247 goto start;
248 goto nodevrandom;
249 }
250 #ifndef O_CLOEXEC
251 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
252 #endif
253
254 /* Lightly verify that the device node looks sane */
255 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
256 close(fd);
257 goto nodevrandom;
258 }
259 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
260 close(fd);
261 goto nodevrandom;
262 }
263 for (i = 0; i < len; ) {
264 size_t wanted = len - i;
265 ssize_t ret = read(fd, (char *)buf + i, wanted);
266
267 if (ret == -1) {
268 if (errno == EAGAIN || errno == EINTR)
269 continue;
270 close(fd);
271 goto nodevrandom;
272 }
273 i += ret;
274 }
275 close(fd);
276 if (gotdata(buf, len) == 0) {
277 errno = save_errno;
278 return 0; /* satisfied */
279 }
280 nodevrandom:
281 errno = EIO;
282 return -1;
283 }
284
285 #ifdef SYS__sysctl
286 static int
getentropy_sysctl(void * buf,size_t len)287 getentropy_sysctl(void *buf, size_t len)
288 {
289 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
290 size_t i;
291 int save_errno = errno;
292
293 for (i = 0; i < len; ) {
294 size_t chunk = min(len - i, 16);
295
296 /* SYS__sysctl because some systems already removed sysctl() */
297 struct __sysctl_args args = {
298 .name = mib,
299 .nlen = 3,
300 .oldval = (char*) buf + i,
301 .oldlenp = &chunk,
302 };
303 if (syscall(SYS__sysctl, &args) != 0)
304 goto sysctlfailed;
305 i += chunk;
306 }
307 if (gotdata(buf, len) == 0) {
308 errno = save_errno;
309 return (0); /* satisfied */
310 }
311 sysctlfailed:
312 errno = EIO;
313 return -1;
314 }
315 #endif /* SYS__sysctl */
316
317 #ifdef HAVE_OPENSSL
318
319 static int cl[] = {
320 CLOCK_REALTIME,
321 #ifdef CLOCK_MONOTONIC
322 CLOCK_MONOTONIC,
323 #endif
324 #ifdef CLOCK_MONOTONIC_RAW
325 CLOCK_MONOTONIC_RAW,
326 #endif
327 #ifdef CLOCK_TAI
328 CLOCK_TAI,
329 #endif
330 #ifdef CLOCK_VIRTUAL
331 CLOCK_VIRTUAL,
332 #endif
333 #ifdef CLOCK_UPTIME
334 CLOCK_UPTIME,
335 #endif
336 #ifdef CLOCK_PROCESS_CPUTIME_ID
337 CLOCK_PROCESS_CPUTIME_ID,
338 #endif
339 #ifdef CLOCK_THREAD_CPUTIME_ID
340 CLOCK_THREAD_CPUTIME_ID,
341 #endif
342 };
343
344 static int
getentropy_phdr(struct dl_phdr_info * info,size_t size,void * data)345 getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
346 {
347 SHA512_CTX *ctx = data;
348
349 SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
350 return 0;
351 }
352
353 static int
getentropy_fallback(void * buf,size_t len)354 getentropy_fallback(void *buf, size_t len)
355 {
356 uint8_t results[SHA512_DIGEST_LENGTH];
357 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
358 static int cnt;
359 struct timespec ts;
360 struct timeval tv;
361 struct rusage ru;
362 sigset_t sigset;
363 struct stat st;
364 SHA512_CTX ctx;
365 static pid_t lastpid;
366 pid_t pid;
367 size_t i, ii, m;
368 char *p;
369
370 pid = getpid();
371 if (lastpid == pid) {
372 faster = 1;
373 repeat = 2;
374 } else {
375 faster = 0;
376 lastpid = pid;
377 repeat = REPEAT;
378 }
379 for (i = 0; i < len; ) {
380 int j;
381 SHA512_Init(&ctx);
382 for (j = 0; j < repeat; j++) {
383 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
384 if (e != -1) {
385 cnt += (int)tv.tv_sec;
386 cnt += (int)tv.tv_usec;
387 }
388
389 dl_iterate_phdr(getentropy_phdr, &ctx);
390
391 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
392 HX(clock_gettime(cl[ii], &ts) == -1, ts);
393
394 HX((pid = getpid()) == -1, pid);
395 HX((pid = getsid(pid)) == -1, pid);
396 HX((pid = getppid()) == -1, pid);
397 HX((pid = getpgid(0)) == -1, pid);
398 HX((e = getpriority(0, 0)) == -1, e);
399
400 if (!faster) {
401 ts.tv_sec = 0;
402 ts.tv_nsec = 1;
403 (void) nanosleep(&ts, NULL);
404 }
405
406 HX(sigpending(&sigset) == -1, sigset);
407 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
408 sigset);
409
410 HF(getentropy); /* an addr in this library */
411 HF(printf); /* an addr in libc */
412 p = (char *)&p;
413 HD(p); /* an addr on stack */
414 p = (char *)&errno;
415 HD(p); /* the addr of errno */
416
417 if (i == 0) {
418 struct sockaddr_storage ss;
419 struct statvfs stvfs;
420 struct termios tios;
421 struct statfs stfs;
422 socklen_t ssl;
423 off_t off;
424
425 /*
426 * Prime-sized mappings encourage fragmentation;
427 * thus exposing some address entropy.
428 */
429 struct mm {
430 size_t npg;
431 void *p;
432 } mm[] = {
433 { 17, MAP_FAILED }, { 3, MAP_FAILED },
434 { 11, MAP_FAILED }, { 2, MAP_FAILED },
435 { 5, MAP_FAILED }, { 3, MAP_FAILED },
436 { 7, MAP_FAILED }, { 1, MAP_FAILED },
437 { 57, MAP_FAILED }, { 3, MAP_FAILED },
438 { 131, MAP_FAILED }, { 1, MAP_FAILED },
439 };
440
441 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
442 HX(mm[m].p = mmap(NULL,
443 mm[m].npg * pgs,
444 PROT_READ|PROT_WRITE,
445 MAP_PRIVATE|MAP_ANON, -1,
446 (off_t)0), mm[m].p);
447 if (mm[m].p != MAP_FAILED) {
448 size_t mo;
449
450 /* Touch some memory... */
451 p = mm[m].p;
452 mo = cnt %
453 (mm[m].npg * pgs - 1);
454 p[mo] = 1;
455 cnt += (int)((long)(mm[m].p)
456 / pgs);
457 }
458
459 /* Check cnts and times... */
460 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
461 ii++) {
462 HX((e = clock_gettime(cl[ii],
463 &ts)) == -1, ts);
464 if (e != -1)
465 cnt += (int)ts.tv_nsec;
466 }
467
468 HX((e = getrusage(RUSAGE_SELF,
469 &ru)) == -1, ru);
470 if (e != -1) {
471 cnt += (int)ru.ru_utime.tv_sec;
472 cnt += (int)ru.ru_utime.tv_usec;
473 }
474 }
475
476 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
477 if (mm[m].p != MAP_FAILED)
478 munmap(mm[m].p, mm[m].npg * pgs);
479 mm[m].p = MAP_FAILED;
480 }
481
482 HX(stat(".", &st) == -1, st);
483 HX(statvfs(".", &stvfs) == -1, stvfs);
484 HX(statfs(".", &stfs) == -1, stfs);
485
486 HX(stat("/", &st) == -1, st);
487 HX(statvfs("/", &stvfs) == -1, stvfs);
488 HX(statfs("/", &stfs) == -1, stfs);
489
490 HX((e = fstat(0, &st)) == -1, st);
491 if (e == -1) {
492 if (S_ISREG(st.st_mode) ||
493 S_ISFIFO(st.st_mode) ||
494 S_ISSOCK(st.st_mode)) {
495 HX(fstatvfs(0, &stvfs) == -1,
496 stvfs);
497 HX(fstatfs(0, &stfs) == -1,
498 stfs);
499 HX((off = lseek(0, (off_t)0,
500 SEEK_CUR)) < 0, off);
501 }
502 if (S_ISCHR(st.st_mode)) {
503 HX(tcgetattr(0, &tios) == -1,
504 tios);
505 } else if (S_ISSOCK(st.st_mode)) {
506 memset(&ss, 0, sizeof ss);
507 ssl = sizeof(ss);
508 HX(getpeername(0,
509 (void *)&ss, &ssl) == -1,
510 ss);
511 }
512 }
513
514 HX((e = getrusage(RUSAGE_CHILDREN,
515 &ru)) == -1, ru);
516 if (e != -1) {
517 cnt += (int)ru.ru_utime.tv_sec;
518 cnt += (int)ru.ru_utime.tv_usec;
519 }
520 } else {
521 /* Subsequent hashes absorb previous result */
522 HD(results);
523 }
524
525 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
526 if (e != -1) {
527 cnt += (int)tv.tv_sec;
528 cnt += (int)tv.tv_usec;
529 }
530
531 HD(cnt);
532 }
533 #ifdef HAVE_GETAUXVAL
534 #ifdef AT_RANDOM
535 /* Not as random as you think but we take what we are given */
536 p = (char *) getauxval(AT_RANDOM);
537 if (p)
538 HR(p, 16);
539 #endif
540 #ifdef AT_SYSINFO_EHDR
541 p = (char *) getauxval(AT_SYSINFO_EHDR);
542 if (p)
543 HR(p, pgs);
544 #endif
545 #ifdef AT_BASE
546 p = (char *) getauxval(AT_BASE);
547 if (p)
548 HD(p);
549 #endif
550 #endif
551
552 SHA512_Final(results, &ctx);
553 memcpy((char *)buf + i, results, min(sizeof(results), len - i));
554 i += min(sizeof(results), len - i);
555 }
556 memset(results, 0, sizeof results);
557 if (gotdata(buf, len) == 0) {
558 errno = save_errno;
559 return 0; /* satisfied */
560 }
561 errno = EIO;
562 return -1;
563 }
564
565 #endif /* HAVE_OPENSSL */
566